Ever since plastics have become a popular material, manufactures have produced a total of 8.3 billion tons of virgin plastic. This is not surprising since the material has many advantages for applications in building and construction, packaging, automotive and medical sectors. The production and usage of plastic materials in all shapes and colors has been a resounding success. However, it is alarming what is happening to the plastic that has served its time.
What happens to waste plastics?
Merely 10 to 16 % of all plastics end up being recycled. The remainder is incinerated for energy recovery or is accumulating in landfills. Up until recently, industrial and household waste was exported to India, China and South-East Asian countries. These countries are preferred due to the low cost of labor, which is critical given the time-consuming process of sorting and separating waste streams typically coming from Europe, the United States and Australia. Changes to the legislations of many of the waste importing countries have resulted in large numbers of plastic waste shipments being turned away. Consequently, the efforts to recycle plastics needs to increase on a global level.
The two prevailing methods to recycle plastics
Chemical or feedstock recycling is the process of changing the chemical structure of plastic waste and converting it into shorter molecules. The monomers can then be used for new chemical reactions. Mechanical recycling refers to the process of producing a re-granulate from the waste material without changing its chemical structure.
Yes, there are challenges in plastic recycling
Plastic recycling is not as easy as recycling metals, which have very different densities, different electrical and magnetic properties, and even different colors. Therefore, it is easy for humans and machines to separate metals from one another and from other materials. Plastics are a whole other story.
Due to the difficulty of separating various types of plastic waste materials, mechanically recycled plastics typically do not have the same degree of purity as virgin materials. Hence, companies are hesitant to use recyclates as they cannot be sure that the batch quality will consistently meet the required material properties of end products.
One would normally expect recycled plastics to have a lower price than virgin material. This is often not the case as the process of shipping it to recycling facilities, washing the waste materials, shredding and re-melting the plastics is complex and thus, rather expensive. Additionally, the quality control and assurance is also linked to further expenses for staff and equipment.
Quality control of recycled plastics with thermal analysis
In order to confirm the quality of recycled plastics as well as to detect and identify potential impurities, appropriate and continuous analysis of the recycled material is required.
Both Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA) are able to identify polymer impurities in recycled materials in a fast and easy way. By using the software feature AutoEvaluation in the NETZSCH Proteus® software, all relevant effects in the measurements curves are detected. The feature Identify feature additionally helps identify, which polymers are included in the sample.
Click here to learn more on how to detect and identify impurities in recycled thermoplastics with DSC and TGA.
Geyer, Roland & Jambeck, Jenna & Law, Kara. (2017). Production, use, and fate of all plastics ever made. Science Advances. 3. e1700782. 10.1126/sciadv.1700782.
Illustration: Hundertmark, T., Mayer, M., McNally, C., Simons, T. J., Witte, C.: How plastics waste recycling could transform the chemical industry. McKinsey & Company. December 2018.